Incomplete combustion of an engine, that is, misfire in which abnormal combustion occurs in a cylinder of the engine, means that fuel injected into the cylinder cannot be completely combusted within a set period of time and is discharged to an exhaust system. When the misfire occurs, while the fuel, which is not completely combusted, is discharged to the exhaust system, serious problems including damage to a catalyst device or an engine output deterioration, and discharge of harmful exhaust gas are caused.
Misfire diagnosis is thus critical for on-board diagnostics (OBD). An OBD system monitors systems associated with exhaust gas and evaporation gas in the operating areas.
In general, the misfire diagnosis is achieved by measuring variation of an angular velocity of a crankshaft. When a road on which a vehicle travels has a rough surface, the angular velocity of the crankshaft varies due to vibration transferred from a wheel of the vehicle. When the misfire diagnosis is performed only by the variation in angular velocity of the crankshaft, it may be misdiagnosed that the misfire occurs even though the misfire does not occur.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.